The invention relates to a connector for optically coupling at least one pair of optical fibers. The end portions of the fibers are accommodated in envelopes having circularly-cylindrical outer surfaces. The connector includes a coupling sleeve for coaxially accommodating at least the free end portions of the two envelopes. The sleeve optically connects the optical fibers via their end faces. The coupling sleeve includes a central cavity which extends in a longitudinal direction. The central cavity is shaped as a prism with a triangular cross-section. An inscribed circle has a diameter which is smaller than the diameter of the outer surface of the envelope. The walls of the central cavity are disposed so as to be resilient in the radial direction so that the envelopes can be clamped in the central cavity.
A connector of this kind is described in U.S. Pat. No. 4,193,665. The coupling sleeve of this known connector consists of a thin-walled cylindrical tube whose walls are deformed in their mid-region so as to form the prismatic central cavity. Such coupling sleeves are particularly suitable for optically coupling fiber bundles in which a large number of optical fibers are accommodated in a common envelope.
In applications where each end portion of an optical fiber is accommodated in an envelope, the accuracy with which the two envelopes are positioned and retained on a common axis is usually insufficient, notably when so-called monomode fibers are concerned. This is probably due to the fact that when one of the three walls of the central cavity is deformed at a point, such deformation may influence all points of all three walls.